In the mutual displacement of bodies it is conventional to apply between them a friction-reducing agent such as oil, grease, soap or the like. A disadvantage with this technique is that the lubricant has a tendency to spread to such places where it is not supposed to be, while also as handling often becomes messy. When the operation which requires the lubricant has been executed, an extra cleaning operation is generally required, in which a solvent of some kind must often be used, and workmen's safety directions relating to air changes etc. must be observed. If one or both bodies is of porous material there is the additional drawback that the lubricant is absorbed by the porous material.